This invention is directed to indicators and more particularly to devices for indicating that a pneumatic structure (tire) is changing shape (deflating).
As will be better appreciated from the following description of a preferred embodiment, the present invention is primarily suitable for use in combination with trailers towed by automobiles, light trucks and the like, and was developed in that environment. However, it also will be appreciated that the invention can be utilized in other environments where it is desired to reliably sense when a pneumatic structure changes from its normal configuration.
Ever since the advent of the automobile, trailers have been utilized to move certain cargo such as homes, boats, etc. As the towing power of the automobile has increased, so has the size and weight of the cargo carried by trailers increased. In recent years, automobiles have been used to tow boat trailers, carrying boats in excess of 20 feet and weighing up to several tons, for example. Large, modern towable house trailers may be of equal size and weight. While an automobile can readily pull trailers carrying objects of this size and weight, certain problems exist that have become more acute as the size and weight of the cargo being carried by the trailer have increased.
More specifically, most trailers include a frame and one or more axles on which pneumatic tires are mounted. Pneumatic tires have the disadvantage that they deflate and go "flat" when they are punctured, either by some external object (e.g., nail) or because of a blowout. While a flat tire is usually only mildly inconvenient when a trailer is stationary, it may become a hazard to both life and property when the trailer is moving. The hazard may be extremely acute if the trailer is carrying a large and heavy cargo, such as a large boat, for example. A deflated pneumatic tire is extremely hazardous in such a case because the mass of the cargo will tend to gyrate back and forth as a result of the instability created by the deflated tire. These gyrations often tend to build in amplitude and can result in not only the destruction of the trailer, but also the destruction of the towing vehicle and, thus, lead to the injury or death of the occupants of the towing vehicle. Consequently, it is desirable to provide a pneumatic tire trouble indicator that indicates to the occupants of the towing vehicle that a pneumatic tire of the trailer has become, or is being, deflated.
Pneumatic tire trouble indicators have been proposed by the prior art. However, they have not been generally commercially accepted because of certain unresolved disadvantages. An example of a prior art tire trouble indicator is described in U.S. Pat. No. 2,457,161 issued to W. C. Laidlaw for "Tire Deflation Switch" on Dec. 28, 1948. The major problem with devices of the type described in this patent relates to their reliability. More specifically, the Laidlaw patent describes a device wherein a rod, located adjacent to a tire, is moved when it contacts the ground. This action occurs when the tire deflates. Movement of the rod causes metal-to-metal contact and current flow through an indicator to occur. One of the major disadvantages to this structure is that the entire switch assembly, including the metal contact elements, are exposed to the atmosphere. Because they are exposed to the atmosphere, they are readily corroded and, thus, rapidly become unreliable. Further, because the exposed switch assembly is mounted near the tire whose inflation it is designed to sense, the assembly, including the metal contact elements are exposed to the dirt, oil, and water sprayed around by tire rotation. These items tend to coat the metal contacts with a non-conductive coating even before they become corroded.
Therefore, it is an object of this invention to provide a new and improved pneumatic tire trouble indicator.
It is a further object of this invention to provide a pneumatic tire trouble indicator that includes a tire deflation sensing switch that is reliable and, suitable for use over extended periods of time without requiring cleaning and maintenance.
It is another object of this invention to provide a new and improved tire deflation sensing switch suitable for sensing when a pneumatic tire, or other pneumatic structure, changes from its normal shape and closing electrical switch contacts when a shape change is sensed.
Another disadvantage of pneumatic tire sensing switches of the type disclosed in the Laidlaw patent relates to their ability to sense in only one plane. In the case of Laidlaw, the sensing plane lies parallel to the plane defined by the associated tire. Single plane sensing has a number of disadvantages. First, it requires that the switch be relatively precisely aligned. Second, it only allows for sensing of one parameter. In the case of Laidlow, the single parameter sensed is the sensing element sliding on the ground. It is more desirable to sense several parameters occurring in different planes. For example, it is desirable to sense the change in the thickness of the lower sidewall of the tire that occurs as it goes flat, as well as its decrease in height.
Therefore, it is an object of this invention to provide a new and improved pneumatic tire deflation switch including a movable switch element that is movable in more than one plane.